With the advent of electronic fuel control systems for internal combustion engines, a sensor for detecting the quantity of air being supplied to the engine is required. This information is required by the electronic fuel control system to accurately control the quantity of fuel being supplied to the engine to maintain the desired air/fuel ratio. In early electronic fuel control systems, the quantity of air being supplied to the engine was computed from the engine speed and absolute pressure of the air in the air intake manifold of the engine. More recently, mass air flow sensors have been developed to measure the mass flow rate of the air through the engine's air intake manifold. For the electronic fuel control system to accurately control the quantity of fuel being delivered to the engine, the mass air flow sensor must be accurately calibrated as a function of mass air flow rates and as a function of temperature.
In the current production of mass air flow sensors, the sensors are loaded into a cold chamber are temperature soaked until they achieve the temperature of the cold chamber. The mass air flow sensors are then manually loaded into a cold test station and its output signal is measured and stored. After the cold test, the mass air flow sensor is removed from the cold test station and placed in a hot chamber where it is temperature soaked until it reaches the temperature of the hot chamber. After reaching the temperature of the hot test chamber, the output signal is measured in a hot test station.
The problem with this method is that the mass air flow rate in the cold and hot test stations are different and as a result the calibration of the mass air flow sensor as a function of temperature is not repeatable making the calibration less than desired for the accurate computation of the fuel for the engine.
The invention is a production test apparatus for measuring the output signals of the mass air flow sensors at two different temperatures in which the air flow rate at both temperatures is the same.